This invention relates generally to robot manipulators and particularly to a system of control for a robot manipulator to pick an individual part from a bin or container of multiple parts.
Bin picking by a robot manipulator in real time is a complex problem for roboticists. No simple sure visual method presently exists to compensate for the problem of overlapping geometry which is encountered in a supply bin of randomly oriented parts. The contemplated solutions to the problem of bin picking and overlapping geometry have required extremely complex image processing systems. One such system is described in an article by Longheed and Sampson, entitled "3-D Imaging Systems And High Speed Processing For Robot Control", Machine Vision And Applications, Vol. 1:41-57 (1988).
These complex image processing systems require a substantial time period to process input data from the video devices. This processing time may be unsatisfactory in a fast paced manufacturing environment. Accordingly, the need for a simple approach is needed in order to provide a real time, economical solution to the overlapping geometry problems encountered in typical manufacturing environments.
It is therefore an object of the present invention to provide a simple, economical control system for readily determining a closest part in a bin of randomly oriented parts.
It is another object of the present invention to provide a bin picking system utilizing acoustic transducers operatively coupled to a video camera.
It is another object of the present invention to provide a system for repetitively grasping individual parts in a predetermined orientation from a bin of unoriented, overlapping parts.
The bin picking system in accordance with the present invention comprises a robot manipulator arm having acoustic transducers mounted thereon, a system controller, a video camera and a laser spotter. The controller directs the movement of the robot manipulator arm, camera and spotter. The camera and spotter are used to locate a feature on an individual part in a bin of randomly oriented parts.
The robot manipulator arm includes a conventional articulated wrist having a gripper assembly attached thereto. The gripper assembly is basically a mechanical hand with a pair of opposing fingers and a centrally mounted acoustic transducer. The acoustic transducer mounted on the robot manipulator arm is used to determine the relative bearing between the robot manipulator arm and the part in the bin closest to the manipulator arm. An array of four acoustic transducers is mounted to the mechanical hand. Each transducer is symmetrically spaced from the center of the mechanical hand. The array is used to determine the aspect, or orientation of the part with respect to the manipulator arm.
The wrist is designed to slue the gripper assembly back and forth over the bin to locate the closest part by virtue of echo location from the central acoustic transducer. The central transducer is activated periodically as the wrist is slued over the bin, using pulses in the two to three kilohertz range. The pulses are spaced in time so as to strike the surface of the bin at approximately one inch intervals. The echoes received back from the bin are evaluated by the controller to determine the closest part by measuring the phase shift of the echoes.
Once the closest part is determined, the controller generates a bearing to this part and sends this bearing to a video camera which is aimed along the bearing. The camera takes a video image or picture of the tentatively identified part. This picture is then compared by the controller module to a stored image of the part in the memory portion of the controller module in order to locate a predetermined feature on the part. When this feature is tentatively identified, another bearing is generated by the control module to the feature. A laser beam is directed along this bearing. The laser beam provides a pin point of light which then is reflected off of the feature and back to the video camera. If the feature has been correctly identified and located, the reflected laser light will have a certain grayscale value.
The video camera receives an image of this reflected laser light and the controller evaluates the intensity of the reflection to determine if it is within the prescribed range of values. If it is, the location of the feature on the part has been confirmed. If it is not, the sequence of steps above described is then repeated for a different area of the bin. Alternatively, the bin may be shaken or shuffled and the above described process is repeated until a part with a given feature is confirmed.
Once confirmation has taken place, the centroid of the part is calculated by the control module and a bearing from the robot manipulator arm to the centroid is determined. The manipulator arm is then driven to a predetermined distance from the centroid and stopped. The planar array of acoustic transducers is then activated to determine the tilt or aspect of the part. An error signal is generated by a comparison of the echo signal intensities to stored expected values at this predetermined distance from the part, and a drive signal is generated which is proportional to the error. The robot manipulator arm is then driven by the error signal until the error signal is nulled.
The position of the robot manipulator arm which nulls the error signal corresponds to the correct position for grasping the part. Once the error signal is nulled, the control module directs the gripper assembly on the end of the robot manipulator arm to grasp the part and then move the part in accordance with the prescribed manufacturing sequence. The above described sequence is then repeated to locate and pick the next and each subsequent part from the bin. The use of acoustic transducers and video thus eliminates the need for a complex 3-dimensional image processing system and simplifies the identification of particular features on a part in a real time processing system.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a consideration of the following detailed description and the appended claims, taken in conjunction with the accompanying drawings.